I. Field of the Invention
This invention relates to molten metal containment structures including refractory or ceramic vessels used for conveying, treating and/or holding molten metals. More particularly, the invention relates to such vessels and sections thereof.
II. Background Art
Metal containment structures such as launders, runners, etc., are often required during casting operations and the like to convey molten metal from one location, e.g. a metal melting furnace, to another location, e.g. a casting mold or casting table. In other operations, metal containment structures are used for metal treatments, such as metal filtering, metal degassing, metal transportation, or metal holding. Metal-contacting vessels, such as troughs, containers, ladles and the like, used in such structures are generally made from refractory materials, and especially ceramic materials, that are resistant to high temperatures and to degradation by the molten metals to which they are exposed. Sometimes, such structures are provided with sources of heat to ensure that the molten metals do not cool unduly or solidify as they are contained within or conveyed through the vessels. The source of heat may be electrical heating elements positioned adjacent to the vessels or enclosures conveying hot fluids (e.g. combustion gases) along the inner or outer surfaces of the vessels.
Refractory vessels used in such structures are subjected to thermal cycling, i.e. significant changes of temperature, when molten metal is being conveyed or when additional heating is applied, or when the vessel sections are idle or allowed to cool. Thermal cycling can cause cracks to form in the refractory material from which the vessels or vessel sections are made. The cracks propagate with time and may eventually become so large and deep that molten metal leaks from the vessels. When this happens, the vessels thus-affected must be repaired or replaced, and often the service lives of such components are quite short. There is therefore a need for ways of extending the effective service lives of molten metal-contacting vessels and sections thereof, and ways of preventing or minimizing crack formation and leakage of molten metal from such vessels.
U.S. Pat. No. 2,301,101, which issued to Lewis T. Welshans on Nov. 3, 1942, discloses a refractory hot top for a casting mold having wire mesh embedded in its walls, but this there is no disclosure of such use in trough sections.
U.S. Pat. No. 5,505,893, which issued to Charles W. Connors, Jr. on Apr. 9, 1996 discloses an open mesh screen used in molding a refractory lining of a trough. However, the screen is removed or dissolved away after the trough has been completed.
Despite these disclosures, there is still a need for improved vessel sections and improved methods of making the same.